520 
fxus61 kphi 220809 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
309 am EST Sat Nov 22 2008 


Synopsis... 
low pressure is well northeast of the region. High pressure, over 
the Tennessee Valley this morning, will build slowly over the area 
into Monday before moving off the Delaware-Maryland-Virginia. Developing storm in 
the Great Lakes will reach Pennsylvania Monday night with its 
attendant cold front reaching the coast late Monday night. 


&& 


Near term /through tonight/... 
it's a cold morning and will be a cool day today. There will be 
light snow showers some northern areas this morning, but no 
nightmare rush hour snow like Friday morning. Our phlpnsphi has 
updated totals with two 4 inch amounts in Chester and Delaware 
co's. The late nam(06z) last night showed a 4 inch amount but 
isolating it was very tough. Anyway, kdix 88d is showing some 
snow showers extending from the Poconos and into northwest New 
Jersey. This will be ongoing for a good part of the day and spread 
a little farther south. The gradient has tightened up especially 
toward the coast and this is pulling cold air down into the 
forecast area. As a result some of the snow bands extending from 
the lakes will probably thin out during the day but still reach 
toward the coast. I have tried to pinpoint the extent of the snow 
on the grids which may look a little awkward. The low pressure is 
well northeast being nudged away by high pressure over the Tennessee 
Valley. Breezy cool conditions today with dew points in the single 
digits to the teens. Highs today ranging from the middle 20s to upper 
30s or lower 40s. 


If you are traveling west and north from this area the weather 
will be colder and the forecast calls for much more snow. 


For tonight, will continue with a slight chance of snow showers 
down through southern New Jersey and ending before daybreak. The 
temperatures will be very cold so even a light covering will be slick. 
Overnight lows will range from 12 to 23 degrees, not counting the 
wind chill factor. 


&& 


Short term /Sunday through Sunday night/... 
as the ridge builds east, the flow will back slightly and the last 
of the light snow bands should move northeast and away sun evening. 
The coldest 80h advection also shifts with clearing skies and 
setting the stage for another unseasonable cold night for Sunday. 
After clearing skies and a high on Sunday of 32 to 45 degrees, 
Sunday nights low will be middle teens to upper 20s. 


Record low temperatures in the Poconos are around 5 degrees for 
today and 14 at Philadelphia and around 17 at Allentown. 


&& 


Long term /Monday through Friday/... 
we are in for a story period Monday night into Tuesday. Before 
then, while the flow at 500 mb becomes zonal, a very strong short 
wave is digging south toward the northwest Great Lakes. The return 
flow from the departing high on the East Coast is bringing warm 
air north through Texas into the plains by late Sunday night. As 
-10c 80h air invades the northern plains, +12 80h air will be 
moving north northeast into the Missouri Valley. The temperatures 
and moisture clash from the Gulf into the Great Lakes while the 
catalyst in the upper atmosphere will push everything east during 
the day on Monday with a variety of weather stemming from winter 
to even convective. 


Monday begins with sunshine and eyes turn east as the strong 
system pushes the cold front through Monday night. The wind fields 
are very strong ahead of this front with 80h winds of 50 to 60 kts 
and 500 mb winds of 70 to 80 kts. Post frontal winds of 100 knots at 500mb. 
The mixed precipitating will be mainly north of the Mason Dixon 
line while the threat for some very strong fast moving thunderstorms will 
be south. This is a fast moving front and likely to produce some 
damaging winds. Thee will be warm air advection at 80h up to +4 
but this should not dampen too much of the wind speeds transferring 
to the surface. 


It may be a little early to be mentioning the convective threat, 
but it has been a very active fall already and these unseasonably 
strong trough can cause significant weather. 


Once the front GOES through the the low rotates to the Hudson 
Valley on Tuesday, the upper closed low counterpart will become 
vertically stacked and rotate very slowly around our forecast area 
with the surface low moving away from the upper low into the 
Atlantic Thursday night. The upper low will take another day 
before joining it over the New England coastal waters. 


The next European model (ecmwf) is farther north north and west with the low after 
Wednesday night. It takes it back toward the northwest and near 
James Bay by Friday morning. 


The temperatures through this period will remain below normal. The 
only day which come close to reaching normal will be Monday with 
the warm air surge ahead of the approaching front. 


&& 


Aviation /05z Saturday through Wednesday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


As the offshore storm continues to intensify and move away from our 
area, high pressure from the west is bringing in drier air. Skies 
cleared over much of the area overnight, although the west northwest 
flow did allow some SC to move back in to our northern and western 
sections. Once the sun begins to works its magic on the atmosphere, 
SC will spread across the entire area. Look for scattered to broken southern 
and eastern sections and broken to overcast northern and western. VFR 
conditions will prevail today, although snow showers and flurries in 
the Poconos could drop conditions to MVFR at times. West-northwest winds will 
increase to 15 to 20 miles per hour with gusts to near 30 miles per hour. Winds will 
diminish after sunset and cloud cover will also decrease. 


Outlook... 
high pressure is forecast to build in from the west for Sunday and 
Sunday night. A cold front is expected to approach from the 
northwest Monday and should reach our region Monday night. There is 
the possibility of rain showers from Monday afternoon into Monday 
night, and perhaps some snow showers late on Monday night into 
Tuesday. 


&& 


Marine... 
the combination of intensifying low pressure well off to our east and 
cold high pressure building in from the west is producing near gale 
force gusts this morning. While a few gale force gusts are possible 
early this morning, frequent gale force gusts over a sustained period 
of time are not expected. Therefore, we will continue to carry a 
Small Craft Advisory for all of our waters. The pressure gradient 
between the low and the high will weaken very slowly later today 
through tonight. Winds will diminish from west to east and from south 
to north later today through tonight. The advisory will end on 
Delaware Bay at 6 PM this evening. On the ocean, south of Little 
Egg Inlet, the advisory will end at midnight. North of Little Egg 
Inlet, it will end at 6 am Sunday. The high pressure system will 
provide tranquil marine weather Sunday into Monday. Complex low 
pressure dropping down from the Great Lakes will bring the next 
threat for inclement weather along with advisory/warning conditions 
late Monday through Tuesday, and possibly beyond. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...Small Craft Advisory until midnight EST tonight for anz450>455. 
Small Craft Advisory until 6 PM EST this afternoon for anz430- 
431. 


&& 


$$ 
Synopsis...eberwine 
near term...eberwine 
short term...eberwine 
long term...eberwine 
aviation...rpw 
marine...rpw 

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